Nahid Azizi; Hamed Joneidi; Khaled Osati
Volume 26, Issue 3 , September 2019, , Pages 717-730
Abstract
This research monitored changes in canopy cover percentage of typical species during a 10-year period in the Ghosheh rangelands to find out the relationship between two important climate variables (precipitation and temperature) and canopy cover changes. Therefore, the canopy cover ...
Read More
This research monitored changes in canopy cover percentage of typical species during a 10-year period in the Ghosheh rangelands to find out the relationship between two important climate variables (precipitation and temperature) and canopy cover changes. Therefore, the canopy cover percentages of six typical species (separately) and annual species (overall) were measured during 10 years at the end of growing season in thirty 2-m2 plots, distributed along two 250–m transect lines. The results demonstrated that the maximum canopy cover percentage for water year 2006-2007 (wet-year) and the minimum value for water year 2012-2013 (drought) were 15% and 5.5%, respectively. The canopy cover percentage modeling was performed based on linear regression method using precipitation and temperature variables. The precipitation of April explained 65% of changes in canopy cover percentage of A. sieberiat 95% confidence level (RRMSE = 0.26 & MAE=0.49). The best simple linear regression model for estimating canopy cover percentage of S. barbata and Z. eurypterum was introduced by total precipitation of March-June and precipitation of March, representing 77% (at 99% confidence level) and 67% (at 95% confidence level) of changes in canopy cover, respectively. Considering the dominant role of A. sieberi, S. barbata and Z. eurypterum in vegetation composition of study areas, it can be concluded that most changes in canopy cover of the studied rangeland are predictable by variabilityofprecipitation during growing seasons.
Shahram Khalighi Sigaroudi; Ali Sadeghi Sangdehi; Khaled Awsati; Usef GHavidel Rahimi
Volume 16, Issue 1 , December 2009, , Pages 44-54
Abstract
Annual rainfall data related to a 26 year period from a number of Mazandaran climatological stations were employed to analyze and model the precipitation toward a determination of drought as well as wet years. Results indicate the occurrence of different intensity drought phenomenon in all stations. ...
Read More
Annual rainfall data related to a 26 year period from a number of Mazandaran climatological stations were employed to analyze and model the precipitation toward a determination of drought as well as wet years. Results indicate the occurrence of different intensity drought phenomenon in all stations. As regards the classification of the annual wet and dry years, normal precipitation among various alternate dry and wet years can be observed with the normal years having more stability and continuity as compared to wet and dry years. The Standardized precipitation Index (SPI) was recognized better and more accurate model compared to the other models because of more potential such as high sensitivity to precipitation variation and more punctual separating of drought and wet year classes in every events.